There are presently communications systems operating via satellite transponders located in a stationary or a high-elliptical orbit.
In the last few years, however, there is great interest in systems of personal communications with direct access by users and with low-orbit satellite transponders, which affords a drastic decrease in the energetics of radio lines and the use of small-size user stations. Such systems hold particular promise for personal communication with the users disposed on mobile objects or in hard-to-reach areas.
It is to be noted at the same time that the low-orbit satellite systems are extremely complicated because at a height of the satellite transponder in the order of 700 to 22000 km, there are considerable movements of the satellite transponder relative to users, resulting in high Doppler shifts of signal frequencies, and a short time period within which satellite transponders remain in the visibility range of the user consequently, complex equipment of satellite transponders and user stations must be used. Considerable problems arise in case it is required to establish continuous and stable communication of the users during any period of time.
Most known in the art are satellite communications systems with direct signal re-relaying by satellite transponders. A class of satellite communications systems is known in which a partial (or complete) processing of signals from the user stations is performed at the satellite transponders.
Systems are also known of the same class which ensure synchronization of not only the receivers of the user stations but their transmitters as well, which makes it possible to simplify the transponder process, which performs processing of signals from many user stations (G. I. Tuzov et al, "Interference immunity of radio systems with composite signals", edited by G. I. Tuzov, M., Radio i svyaz publishers, 1985, pp 130-132).
There are disclosures of a number of specific satellite low-orbit telephone communications systems. Thus, in the application of "Motorola satellite communication Inc." for the low-orbit communications system, "IRIDIUM" submitted to FCS , Washington, USA, 1990, by the inventors Golsky L. S., Malet F. I., Mutke A. M. is disclosed a communications system including 66 satellite transponders, which ensures global cellular personal telephone communications. This system is disadvantageous in that it has a low level of noise immunity and electromagnetic compatibility, which is defined by the shape of the simple signals used in the system and by the problems in implementing the specific in addition, the system suffers from cellular structure low level of privacy of talks without application of specialized means.
In the application of "Loral cellular systems, corp.," for the system "Globalstar " submitted to FCS , Washington, USA, 1991, by the inventors L. K. Smith, R. M. Halperin, L. A. Taylor, is disclosed another form of a low-orbit satellite communications system. This system is most close to the method of the present invention by the technical essence, shape of the signals used and the effect obtained. Both the method of the present invention and the prior-art method use wide-band pseudorandom phase-shift keyed signals.
Among the disadvantages of the prior-art method is the presence of regional stations providing for control of the communications system and switching of signal flows at satellite transponders, which, though simplifying the transponder design, results, however, in narrowing the area and time of service (communication is ensured only under the condition of transponder visibility at an angle of elevation greater than the limiting one from three points simultaneously, namely, two points of location of the user stations and the point of location of the regional station), and also in increasing signals delay along their propagation route. Among the disadvantages of the prior-art method is also the limitedness of the area of servicing the users and impossibility of effecting global communication.
Considerable difficulties arise in providing continuous communication in the system, which presupposes synchronous transfer of the relaying functions from one (flying past) satellite transponder to another (flying next) at the user stations arbitrarily disposed in the service area. In this case continuity of communication can be provided under the condition of simultaneous visibility (at least during a short time period) of the two satellite transponders following one the other from three points at once, namely, two points of location of the user stations and the point of location of the regional station. In this case the necessity arises of either increasing the number of the satellites in the orbit or of increasing the number of regional stations, which results in greater costs and makes the communications system more complicated. It is to be noted that the level of electromagnetic compatibility (EMC) in the "Globalstar" system is not high because multiple circulation of the signal flows takes place between the Earth and satellite transponder. The disadvantages of this form of the communications system are also not high level of noise immunity, in particular, along the channels of synchronization and service communication, the serviceability of the entire system being dependent on the adequate operation of these channels; there is no solutions at the system level aimed at increasing the privacy of the communication while the numerous users of the system have identical receiving-transmitting subscribers' stations.
One more specific feature of the low-orbit satellite communications systems "Globalstar" and "IRIDIUM" is to be noted, which is associated with the possibility of determining the coordinates by each user from the results of processing the signals coming from a satellite transponder (this is connected mainly with measuring the Doppler frequency in several points of the orbit). This is necessary, first, for the operation of the low-orbit communications system itself because it permits of fixing the user station to a quite definite area on the Earth's surface, and, second, considering the mobility of some user stations, permits the users themselves to establish their position without using specialized navigation means. Not high accuracy of self-location must be listed among the shortcomings of the approach adopted in these systems. On the other hand, a differential method of self-location is known, which is one of the ways for further development of the existing navigation satellite systems of "Glonass" sad "GPS" type. The method resides in that the receiver of one of the said navigation systems is disposed in a reference point with exactly known coordinates. Such a receiver, by receiving signals from a constellation of navigation satellites, solves the problem of assessing the coordinates of the reference point. After comparing the obtained coordinates with the exact coordinates, corrections are calculated, which are transmitted to the navigation information consumers (mainly, to mobile consumers) who are in the vicinity of the reference point at distances within hundreds kilometers. Utilizing the received corrections, the consumers of the navigation satellite systems are capable of improving the accuracy of self-location by one or two orders of magnitude as compared with assessing the coordinates by the navigation satellites only. Implementation of this method is only possible with a developed mobile communications system and with the possibility of ensuring broadcast transmission. Therefore, the subject of the present invention is intended to improve the accuracy of navigation aids for the mobile users of the low-orbit communications system, which widens the potentialities and service properties of the low-orbit satellite communications systems.
The above-mentioned method of establishing communication with the use of "Globalstar" system, allowing the service area widening and calling for the presence of regional stations which ensure going into the network associated with a stationary satellite, makes it possible to provide global communication and can be considered as the most close to the method of multiple-station communication with integration of low-orbit and high-orbit satellite systems.
The communication of two users of the low-orbit system is implemented through the following chain: a user station, a low-orbit transponder, a regional station, a stationary satellite transponder, another regional station, a low-orbit satellite transponder, a user station. In order to establish global communication, another stationary satellite may be needed, which is connected via an intersatellite link with the first stationary satellite.
In this case, with due regard for the signal delay on the time of propagation of radio waves and also because of the numerous reswitchings and rerelayings and also delays in vocoders, the total signal delay will exceed the normal value 0.39 s admissible according to MCCTT, which is a shortcoming of the prior-art method. Listed among other disadvantages must be complexity of the system directly because of the great number of rerelayings and reswitchings, losses in the characteristics of the electromagnetic compatibility (EMC) and noise immunity caused by multiple circulation of signal flows, an insufficient level of unification of the low-orbit and high-orbit communications systems owing to the different principles of their structure (multiple station access, kinds of signals, encoding), narrowing the service area of the low-orbit systems because of the presence of regional stations.
Known in the art is the design of the satellite communications systems which ensure synchronization of both the receivers of the user stations and the transmitters thereof.
The transmitters of the user stations are synchronized due to the auto tuning of the transmitters by the carrier frequency and signal delay (code delay).
There are known two basic types of transponders: those which perform direct relaying of user station signals and those which process the signals on board the satellite transponders. When processing signals at the satellite transponders, a higher noise immunity of the system is provided.
In order to synchronize receiver, and transmitters, use is often made of phase-modulated wideband pseudorandom signals having adequate correlation properties. However, with any signal shapes, measures must be taken on signal search and initial synchronization of receivers and transmitters.
As a result of signal search, narrowing of uncertainty is achieved in evaluating the delay and frequency of the pseudorandom signals to values ensuring the signal capture by correlation tracking systems which include systems of phase (or frequency) auto tuning of frequency and circuits for tracking the delay. It is required to provide the search and initial synchronization of the correlation receiver and transmitter at the user station. The systems of search and initial synchronization of the correlation receivers are described in sufficient detail, for example, in the publication "Interference immunity of radio systems with composite signals", G. I. Tuzov, V. A. Sivov, V. I. Prytkov et al, edited by G. I. Tuzov, M., Radio i svyaz publishers, 1985, pp 115-157. Some of said forms of signal search can be used for search and initial synchronization of the transmitters and communications channel as a whole with the search apparatus disposed at a satellite transponder. In the above-mentioned system, however, the receiver of the satellite transponder becomes seriously complicated and, as a result, the advantage is lost connected with simiplification of the satellite transponder equipment performing auto tuning of all the user stations transmitters. This is attributed to that the search and initial synchronization of the channels need be conducted for the multitute of signals simultaneously arriving from the user stations, and each search period will include, in addition to the time of averaging in the receiver, also the time of propagation of the signal to the satellite transponder and in the backward direction. At the stage of search and initial synchronization of the channels, it is also necessary to have a duplex operation between the satellite transponder and each user station by means of which it will be needed to transmit, from the satellite transponder to the user stations, the information on the instant delay evaluations and signal frequency and to receive the response of each user station, which is not always realizable. Under these conditions, the noise immunity of the communications system in the mode of search and initial synchronization of the channels will obviously be low.
An object of the invention is to provide a method and apparatus for multiple-station communication, which will ensure:
higher noise immunity both through the channels of synchronization and service information transmission and through the channels of the main information transmission; PA1 higher electromagnetic compatibility (intersystem and intrasystem), particularly necessary in repeat use of an engaged frequency band: PA1 increased communication stability including an increase in the area and time of service with considerable dynamics of motion of transponders with respect to the users; PA1 increased privacy of talks and intrasystem electromagnetic compatibility when the users have a large number of identical stations which are randomly disposed; PA1 a decrease in the time of signal search and initial channel synchronization; PA1 a decrease in the time of signal delay along the path of their preparation between the user stations; PA1 simplification and unification of the equipment of satellites transponders and ground-based equipment; PA1 widening of the possibilities of self-location of the communications system users.
This and other objects are accomplished in a method of multiple-station communication for low-orbit satellite systems, comprising the steps of transmitting by user stations synchronization signal and information-modulated signals, reswitching the information-modulated signals aboard a transponder, emitting thereof at different frequencies by beams spaced apart with the use of phase-shift keying, emitting by the transponder its own synchronization signal, receiving the synchronization signal from the satellite transponder by the user stations and the information-modulated signals meant therefor, the method further comprising, according to the invention, generating and emitting, at the satellite transponder, a wideband pseudorandom synchronization signal with phase-shift keying over the entire width of the transmission spectrum from the satellite transponder and over the entire service area divided into cells with the power density gradually increasing from the area center to the edges thereof, modulating said synchronization signal with service information intended for control of the communication system, performing rejection of said synchronization signal spectrum sections coincident, at the time of emission, with the spectrum of signals emitted by the satellite transponder and carrying information, with the emitted power of the synchronization signal being constant, checking at the satellite transponder the location of all the user stations with respect to the spatial cells formed by the beams of an on-board antenna of the satellite transponder, receiving information packets from the user stations and storing the information portion thereof, determining from the packet preambule the carrier-frequency and code-delay mismatches against standards disposed at the satellite transponders, with subsequent storage thereof, retrieving from the memory, shaping and emitting groups of information packets within preset time intervals, meant to be transmitted into different spatial cells with preambles including mismatches for each user station, all the user stations performing reception of the synchronization signal from the satellite transponder and separation of service information with simultaneous rejection of the synchronization signal spectrum portion coincident with the spectrum of the signals carrying information from that spatial cell in which the particular user station is located, performing compensation for the Doppler shift in autotune transmitters using the synchronization signal received from the satellite by the carrier and clock frequencies, transponder, performing autotuning of the own transmitters by the carrier frequency and code delay with the use of mismatch values separated from said preambule, sending a query to the transponder on the necessity of communication with other user stations by emitting, by the auto tune transmitters, several cycles of the pseudorandom radio signal with the code assigned for the call of the satellite transponder with a delay individually preset for each of the user stations, identifying at the satellite transponder the number of the calling user station and the spatial cell in which it is disposed by the received call signal and its delay, reporting by means of the calling user station code the time interval alloted thereto and the internal code for two-way communication with the satellite transponder, the number of the called user station identified at the satellite transponder with its coordinates and the spatial location cell being reported to the satellite transponder from the calling user station within the time interval allotted thereto by modulating the internal code, with the called user station being disengaged, a call arrives from the satellite transponder with the use of its subscriber's code, said call presetting at the same time the time interval end internal code for the two-way communication with the satellite transponder, performing the initial synchronization of the auto tune transmitter from the called user station after receiving a call from the satellite transponder, and reporting to the satellite transponder within the alloted time interval on readiness for communication by modulating the assigned internal code and thereafter separating at the satellite transponder and reporting to the two user stations the time intervals and the numbers of the internal codes to establish two-way communication, the time intervals being assigned proceeding from the condition of convenience of routing the packets taking into consideration the cells of location of the user stations, establishing thereafter the internal codes in the transmitter and receiver at each user station, providing information shaping in a digital form and the time compression thereof, performing multibase coding of the information bar the allocated internal code and emitting a signal within the allotted time interval with a preamble including several cycles of the internal code with a fixed delay (or several cycles of the code allotted to a group of user stations), and performing at the user stations separation of the packets intended therefor, demodulation, decompression and separation of information transmitted to the user stations.
It is preferable that in the method of multiple-station communication for low-orbit satellite systems, according to the present invention, the code allotted to the user station for calling the satellite transponder with the delay established individually for each user station is additionally modulated by a short message including information on the number of the called party, with subsequent demodulation and separation of said message at the satellite transponder.
It is expedient that in the method of multiple-station communication for low-orbit satellite systems, according to the present invention, an intersatellite communication is established with neighbour satellite transponders similar to the communication established between the satellite transponder and one of the user stations, each of the satellite transponders performing, in this case, by the principle of constructing the network, both the part of a user station synchronized from the neighbour satellite tranponder and a satellite transponder from which are synchronized other satellite transponders, and the time of exit from the common service area of each of the user stations and from the spatial cell is determined at the satellite transponders, each of the user stations being informed about this, with simultaneous presenting thereto recommendation on switchover to communication with the most favourable satellite transponder at a new frequency and time interval of another spatial beam, whereupon at the user station, simultaneously with maintaining the communication, a synchronization signal is received from the recommended satellite, with establishing a new frequency and time interval and the auto tune transmitter is synchronized from said satellite transponder by frequency and delay, information is transmitted for some time to both the satellite transponders, and matching of the passage of information flows from the user stations in time is provided at the satellite transponders with the use of intersatellite communications lines, and after that synchonous automatic switchover of the user stations is effected to the communication via the new satellete transponder only.
It is preferable that in the method of multiple-station communication for low-orbit satellite systems, several information packets are transmitted by different internal codes in the same time intervals, the levels of the input signals are measured at the satellite transponder, higher-, lower-power signals being compressed are determined and the levels of the power correction are transmitted in the preamble, and the user stations control the power of their transmitters
It is also preferable that in the method, according to the invention, information is transmitted, from the users disposed in reference points with precisely known coordinates, about the coordinates of said reference points and the navigation corrections obtained as a result of comparison of the precisely known coordinates with those obtained as a result of estimations from navigation satellites, said information is demodulated at the satellite transponder with subsequent modulation by said information of the synchronization signal emitted from the satellite transponder and demodulation of said information by interested user stations.
It is of benefit that in the method of multiple-station communication for low-orbit satellite systems, according to the invention, at the satellite transponder, navigation information is switched which is obtained from the user stations disposed in reference points with precisely known coordinates, and it is transmitted by each of the spaced apart beams within the predetermined time intervals and the allocated internal codes with subsequent separation of said information by interested user stations.
The above-mentioned and other objects are also achieved in a method of multiple-station communication with integration of high-orbit and low-orbit satellite systems which comprise satellite transponders in stationary and low orbits, which method comprises the steps of emitting synchronization signals and information-modulated signals generated on the basis of wideband pseudorandom signals with phase-shift keying, and also receiving information-modulated signals from low-orbit satellite transponders by means of small-size user stations and synchronization signals, which also comprises, according to the present invention, generating, at high-orbit satellite transponders, a wideband pseudorandom synchronization signal with phase manipulation over the entire spectrum width allotted for information transmission from the satellite transponder with code differentiation of signals generated by different satellite transponders, emitting said signal over the entire common spatial service area divided into cells and including visible orbits of all low-orbit satellite transponders, with the power density gradually increasing from the area center to the edges thereof, modulating said signal with service information, performing rejection of said signal spectrum sections coincident at the emission instants with the spectrum of the emitted signals proper which carry information, with the output power of the synchronization signal being maintained constant, performing reception of signal packets from the low-orbit satellite transponders with storage of the information portion thereof, determination from the preamble of said packets the delay and frequency mismatches against standards disposed at the satellite transponders, with subsequent shaping of preambles from the mismatches, and storage of the preambles at the satellite transponders, performing reswitching of the stored information portions of the packets assigned for the user stations of the low-orbit communications system and packet groups to be transmitted to various spatial cells in which are disposed the corresponding satellite transponders of the low-orbit system, forming partially overlapping spatial emission cells by means of a multi-beam transceiving antenna providing a full coverage of the entire service area, the major axes of said cells being parallel to the directions of motion of the satellite transponders of the low-orbit system, performing control over the current position of the satellite transponders with respect to the spatial service cells, effecting reception of the synchronization signal at the low-orbit satellite transponders with separation of service information, conducting rejection of said signal spectrum section coincident with the spectrum of the packets received at that time, performing reception of the packets of high-orbit satellite transponders with separation of the information assigned thereto, performing, at each of the satellite transponder of the low-orbit system, synchronization of its own transmitter by the delay of the emitted signal code and frequency with the use of the corresponding mismatches from the separated packet preamble and with preliminary compensation of the Doppler shift by the carrier and clock frequencies, the value of said compensation being obtained from the received synchronization signal, forming a beam of the transceiving antenna to the corresponding high-orbit satellite transponder from calculated data of the relative position of the satellite and/or from the estimations of the power maximum of the received synchronization signal, said beam being formed wide in the direction of the satellite transponder motion and narrow in the perpendicular direction, emitting, from a low-orbit satellite transponder, in order to call a high-orbit satellite transponder on a request of a user station of the low-orbit system to establish communication, several cycles of the pseudorandom signal, which are allotted for a call, said signal being synchronized from a common clock generator of a transmitter with a delay individual for each low-orbit satellite transponder, modulating said signal with information on the number of the called user station, identifying the number of the calling satellite transponder by the call signal received at the high-orbit satellite transponder and obtaining information on the number of the called user station, determining for communication the satellite transponder of the low-orbit system and reporting thereto the number of the called user station in the user code of said satellite transponder, receiving the call at the satellite transponder of the low-orbit system, relaying the call to the corresponding user station, and, with the readiness of the station, assigning and transmitting, at the calling and called satellite transponders of the low-orbit system, the internal codes and time intervals from said satellites for two-way communication, which are established by the user stations at the low- and high-orbit satellite transponders.
The above-mentioned and other objects are accomplished also in a method of search and initial synchronization of channels in a satellite communications system with direct relaying of signals, in which wideband pseudorandom signals are used for synchronization, and synchronization of the user station transmitters are carried out by a synchronization signal from the satellite transponder, said method providing emission by each user station, in addition to an information-modulated signal, of its own synchronization signal, reception from the satellite transponder of information-modulated signals and its own synchronization signal, the method further comprises, according to the invention, performing at the user stations, after receiving the synchronization signal of the satellite transponder, unidirectional discrete scanning of the delay of the emitted synchronization signal with preliminary compensation of the Doppler increment by the carrier and clock frequencies, which increment is separated from the received synchronization signal of the satellite transponder, noting the instant of coincidence of the own relayed synchronization signal delay with the delay of the reference signal of the same waveform phased from the synchronization signal of the satellite transponder received by the receiver, varying at that instant the direction of scanning to the opposite, again noting the instants of coincidence of the delays of said signals, ceasing scanning at a K-th instant of coincidence of the delays, calculating the number of the steps of scanning between the first and the K-th instants of coincidence of the delays, then inputting the delays into the emitted synchronization signal in the initial direction of scanning by a value equal to half the calculated number of the scanning steps between the first and the K-th coincidence of the delays, where K=2 with (.tau./T)&lt;1 and K=N+1 with (.tau./T).gtoreq.1, where T is the time of exhaustive search of all possible delays of the signal, .tau. is the time of propagation of the signal in forward and reverse directions, N is the integral part (.tau./T).
It is preferable that in the method of search end initial synchronization of channels in the satellite communications system, according to the invention, with the a priori known signal delay on the route (or distance to the transponder) a delay is introduced into the emitted signal at the user station with a reverse sign relative to the received synchronization signal, said delay being proportional to -(.tau./2).sub.ap .-+..DELTA.!, where (.tau./2).sub.ap is the a priori known delay, .DELTA. is the maximum value of the a priori error in the knowledge of the delay, and scanning is commenced in the direction .+-..DELTA., the instant of coincidence of the delays is noted of the own relayed signal received by the receiver and of the reference signal of the same waveform phased from the satellite transponder synchronization signal received by the receiver, the discrete delay 2(.tau./2).sub.ap .+-..DELTA.! is introduced into the emitted signal and scanning is performed in the direction .-+..DELTA., a new instant of coincidence of the signal delays is noted, the resultant is estimated taking into account the scanning of delay between the instants of coincidence of the delays of the reference and relayed signals, and then a discrete introduction of the delay is performed in the initial direction, said delay being equal to half the resultant delay.
It is also expedient that in the method of the present invention, at the satellite transponder with signal processing, the instants of coincidence of the delays of the synchronization signal emitted by the user station and the reference signal of the same waveform are noted, which reference signal is phased from a generator of the synchronization signal codes disposed at the satellite transponder, and the instants of coincidence of the delays are subsequently relayed by modulating the signal from the satellite transponder, the signal is received and demodulated by the appropriate user stations.
The above-mentioned and other objects are also accomplished in that in an apparatus for implementing the method of multiple-station communication for low-orbit satellite systems, which comprises, at a satellite transponder, a transceiving phased antenna array with a modulator and a high-frequency portion, a receiver of signals of communication and service information, a unit for generating a synchronization signal and a service information signal, a frequency spectrum synthesizer, an antenna for transmitting a signal of synchronization with a high-frequency portion, a unit for packet generating with a buffer memory, a user station including a transceiving antenna with a high-frequency portion of a transmitter, a signal receiver with a high-frequency portion and channels for separating information, a synchronization signal receiver comprising a circuit for phase autotuning of frequency, a delay tracking circuit, interconnected by a cross link, and a channel for service information separation; a transmitter with frequency end code delay autotuning, including a frequency auto tune circuit and a delay tracking circuit, a unit for generating digital information with a device for compressing thereof, a buffer memory and a packet shaper, a control unit, according to the present invention, installed at the satellite transponder between the synchronization signal generating unit and the antenna for transmitting the synchronization signal are rejection filters connected through a control input with a control unit, frequency and delay discriminators are introduced, which are connected to the buffer memory and a preamble shaper and have their input and output connected, respectively, to a linear output of the receiver of communication and service information signals and to an input of the packet generator with the buffer memory, the output of the packet generator being connected to the transceiving phased array with the modulator and high-frequency portion, there ere introduced generators of a synchronization code, internal and user codes controlled from a single clock generator and phased with each other, the internal code generator being connected to the packet generator and frequency and delay discriminators with the buffer memory and the preamble shaper, a receiver of a call of the satellite transponder is incorporated, which is a matched filter connected, through an input, to the receiver of communication and service information signals, and, through outputs, to the control unit and to a user station call generator, a unit for compensating the Doppler shift being installed at the user station, installed between the circuit of phase auto tune of frequency and the signal receiver with the high-frequency portion and information separation channels are rejection filters having their input connected to an output of the control unit; gerators of a synchronization code, user codes and internal codes synchronized and phased between each other are incorporated into the circuit for tracking the delay of the receiver synchronization signal, the internal code generator being coupled to a delay discriminator of the transmitter with frequency and code delay autotuning, introduced into the circuit for tracking the delay of the auto tune transmitter is a code generator for calling the transponder and an internal code generator synchronized and phased with each other and a series combination of a voltage adder, a clock frequency generator and a scanning circuit having its output coupled to an input of the generator of call code of the transponder and the internal codes of the auto tune transmitter, and having its input connected to an output of a circuit for search and initial synchronization of the transmitter having its input connected to an output of the signal receiver with the high-frequency portion and information separation channel, incorporated in the circuit for autotuning the transmitter is a voltage adder having its output connected via a controlled generator, as is the output of the controlled clock frequency generator of the autotune transmitter, to the Doppler shift compensation unit.
The above-mentioned and other objects are further accomplished in that in an apparatus for signal search and initial channel synchronization in a satellite communications system, comprising, at a user station, a circuit of phase auto tune of frequency, including a series combination of a signal receiver with a high-frequency portion, injection filters, a subtractive mixer, a code demodulator with an intermediate frequency amplifier, a phase detector with a lowpass filter, a controlled generator coupled to a reference input of the subtractive mixer, a frequency spectrum synthesizer, a delay tracking circuit, including a series combination of a discriminator with a lowpass filter, a controlled generator, a synchronization code generator connected to a reference input of the discriminator, and generators of transmitter codes (user and internal); a circuit of phase (frequency) auto tuning of the transmitter frequency, including a phase (frequency) discriminator with a lowpass filter, a controlled generator, a modulator and an amplifier of high frequency; a circuit for tracking a transmitter delay code, including a delay discriminator with a lowpass filter, a controlled clock frequency generator, generators of a transmitter code (call of a transponder and internal codes), said transmitter being coupled to a modulator with a high-frequency amplifier, the inputs of of the phase (frequency) discriminator with a lowpass filter and of the delay discriminator with a lowpass filter being coupled to the signal receiver with a high-frequency portion, and the input of the discriminator with a lowpass filter being connected to the output of the subtractive mixer, according to the present invention, a Doppler shift compensation unit is introduced, which is made up of two identical circuits which comprise subtractive mixers; phase detectors with lowpass filters, a voltage adder, the inputs of the subtractive mixer in the first circuit being connected to the outputs of the controlled generator and to the corresponding output of a frequency spectum synthesizer, and the second input of the phase detector with a lowpass filter is connected to the output of the controlled generator, and the inputs of the subtractive mixer in the second circuit being connected to the output of the controlled clock generator and to the corresponding output of the frequency spectrum synthesizer, and the second input of the phase detector with a lowpass filter is connected to the output of the controlled clock frequency generator, said voltage adder of the first circuit being included into the circuit of phase (frequency) auto tuning of the transmitter frequency between the input of the controlled generator and, through a switch K, the output of the phase (frequency) discriminator with a lowpass filter, and said voltage adder of the second circuit being included into the code delay tracking circuit of the transmitter between the input of the controlled clock frequency generator and, through a second switch K, the output of the delay discriminator with a lowpass filter, a circuit for signal search and initial synchronization of the transmitter, which circuit is a series combination of a search correlator and a search mode control unit coupled to a scanning circuit, the input of the search correlator being connected to the output of the signal receiver with a high-frequency portion and to the reference output of the internal code generator of the transmitter, and the second and third inputs of the search mode control unit being connected to the outputs of the controlled clock generator and the reference output of th,e internal code generator of the transmitter, and the control output of the search mode control unit being connected to the switches K, the scanning circuit being connected between the input of the generators of the transmitter code of the transponder call and of the internal codes and the output of the controlled clock frequency generator.